package test.skymobi.http.file;

import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.handler.codec.http.*;
import io.netty.handler.stream.ChunkedFile;
import io.netty.util.CharsetUtil;

import javax.activation.MimetypesFileTypeMap;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.RandomAccessFile;
import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.text.SimpleDateFormat;
import java.util.*;
import java.util.regex.Pattern;

import static io.netty.handler.codec.http.HttpHeaders.Names.*;
import static io.netty.handler.codec.http.HttpHeaders.isKeepAlive;
import static io.netty.handler.codec.http.HttpHeaders.setContentLength;
import static io.netty.handler.codec.http.HttpMethod.GET;
import static io.netty.handler.codec.http.HttpResponseStatus.*;
import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;

public class HttpStaticFileServerHandler extends ChannelInboundHandlerAdapter {

	public static final String HTTP_DATE_FORMAT = "EEE, dd MMM yyyy HH:mm:ss zzz";
	public static final String HTTP_DATE_GMT_TIMEZONE = "GMT";
	public static final int HTTP_CACHE_SECONDS = 60;

	@Override
	public void channelRead(ChannelHandlerContext ctx, Object obj) throws Exception {

		FullHttpRequest request = (FullHttpRequest) obj;

		if (!request.getDecoderResult().isSuccess()) {
			sendError(ctx, BAD_REQUEST);
			return;
		}

		if (request.getMethod() != GET) {
			sendError(ctx, METHOD_NOT_ALLOWED);
			return;
		}

		final String uri = request.getUri();
		final String path = sanitizeUri(uri);
		if (path == null) {
			sendError(ctx, FORBIDDEN);
			return;
		}

		File file = new File(path);
		if (file.isHidden() || !file.exists()) {
			sendError(ctx, NOT_FOUND);
			return;
		}

		if (file.isDirectory()) {
			if (uri.endsWith("/")) {
				sendListing(ctx, file);
			} else {
				sendRedirect(ctx, uri + '/');
			}
			return;
		}

		if (!file.isFile()) {
			sendError(ctx, FORBIDDEN);
			return;
		}

		// Cache Validation
		String ifModifiedSince = request.headers().get(IF_MODIFIED_SINCE);
		if (ifModifiedSince != null && !ifModifiedSince.isEmpty()) {
			SimpleDateFormat dateFormatter = new SimpleDateFormat(HTTP_DATE_FORMAT, Locale.US);
			Date ifModifiedSinceDate = dateFormatter.parse(ifModifiedSince);

			// Only compare up to the second because the datetime format we send to the
			// client
			// does not have milliseconds
			long ifModifiedSinceDateSeconds = ifModifiedSinceDate.getTime() / 1000;
			long fileLastModifiedSeconds = file.lastModified() / 1000;
			if (ifModifiedSinceDateSeconds == fileLastModifiedSeconds) {
				sendNotModified(ctx);
				return;
			}
		}

		RandomAccessFile raf;
		try {
			raf = new RandomAccessFile(file, "r");
		} catch (FileNotFoundException fnfe) {
			sendError(ctx, NOT_FOUND);
			return;
		}
		long fileLength = raf.length();

		FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, OK);
		setContentLength(response, fileLength);
		setContentTypeHeader(response, file);
		setDateAndCacheHeaders(response, file);
		if (isKeepAlive(request)) {
			response.headers().add(CONNECTION, HttpHeaders.Values.KEEP_ALIVE);
		}

		// Write the initial line and the header.
		ctx.write(response);

		// Write the content.
		ChannelFuture writeFuture = ctx.write(new ChunkedFile(raf, 0, fileLength, Integer.MAX_VALUE));

		// Decide whether to close the connection or not.
		if (!isKeepAlive(request)) {
			// Close the connection when the whole content is written out.
			writeFuture.addListener(ChannelFutureListener.CLOSE);
		}
	}

	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
		cause.printStackTrace();
		if (ctx.channel().isActive()) {
			sendError(ctx, INTERNAL_SERVER_ERROR);
		}
	}

	private static final Pattern INSECURE_URI = Pattern.compile(".*[<>&\"].*");

	private static String sanitizeUri(String uri) {
		// Decode the path.
		try {
			uri = URLDecoder.decode(uri, "UTF-8");
		} catch (UnsupportedEncodingException e) {
			try {
				uri = URLDecoder.decode(uri, "ISO-8859-1");
			} catch (UnsupportedEncodingException e1) {
				throw new Error();
			}
		}

		if (!uri.startsWith("/")) {
			return null;
		}

		// Convert file separators.
		uri = uri.replace('/', File.separatorChar);

		// Simplistic dumb security check.
		// You will have to do something serious in the production environment.
		if (uri.contains(File.separator + '.') || uri.contains('.' + File.separator) || uri.startsWith(".")
				|| uri.endsWith(".") || INSECURE_URI.matcher(uri).matches()) {
			return null;
		}

		// Convert to absolute path.
		return System.getProperty("user.dir") + File.separator + uri;
	}

	private static final Pattern ALLOWED_FILE_NAME = Pattern.compile("[A-Za-z0-9][-_A-Za-z0-9\\.]*");

	private static void sendListing(ChannelHandlerContext ctx, File dir) {
		FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, OK);
		response.headers().add(CONTENT_TYPE, "text/html; charset=UTF-8");

		StringBuilder buf = new StringBuilder();
		String dirPath = dir.getPath();

		buf.append("<!DOCTYPE html>\r\n");
		buf.append("<html><head><title>");
		buf.append("Listing of: ");
		buf.append(dirPath);
		buf.append("</title></head><body>\r\n");

		buf.append("<h3>Listing of: ");
		buf.append(dirPath);
		buf.append("</h3>\r\n");

		buf.append("<ul>");
		buf.append("<li><a href=\"../\">..</a></li>\r\n");

		for (File f : dir.listFiles()) {
			if (f.isHidden() || !f.canRead()) {
				continue;
			}

			String name = f.getName();
			if (!ALLOWED_FILE_NAME.matcher(name).matches()) {
				continue;
			}

			buf.append("<li><a href=\"");
			buf.append(name);
			buf.append("\">");
			buf.append(name);
			buf.append("</a></li>\r\n");
		}

		buf.append("</ul></body></html>\r\n");

		response.content().writeBytes(Unpooled.copiedBuffer(buf, CharsetUtil.UTF_8));

		// Close the connection as soon as the error message is sent.
		ctx.write(response).addListener(ChannelFutureListener.CLOSE);
	}

	private static void sendRedirect(ChannelHandlerContext ctx, String newUri) {
		FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, FOUND);
		response.headers().add(LOCATION, newUri);

		// Close the connection as soon as the error message is sent.
		ctx.write(response).addListener(ChannelFutureListener.CLOSE);
	}

	private static void sendError(ChannelHandlerContext ctx, HttpResponseStatus status) {
		FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, status);
		response.headers().add(CONTENT_TYPE, "text/plain; charset=UTF-8");
		response.content()
				.writeBytes(Unpooled.copiedBuffer("Failure: " + status.toString() + "\r\n", CharsetUtil.UTF_8));

		// Close the connection as soon as the error message is sent.
		ctx.write(response).addListener(ChannelFutureListener.CLOSE);
	}

	/**
	 * When file timestamp is the same as what the browser is sending up, send a
	 * "304 Not Modified"
	 *
	 * @param ctx
	 *            Context
	 */
	private static void sendNotModified(ChannelHandlerContext ctx) {
		HttpResponse response = new DefaultHttpResponse(HTTP_1_1, NOT_MODIFIED);
		setDateHeader(response);

		// Close the connection as soon as the error message is sent.
		ctx.write(response).addListener(ChannelFutureListener.CLOSE);
	}

	/**
	 * Sets the Date header for the HTTP response
	 *
	 * @param response
	 *            HTTP response
	 */
	private static void setDateHeader(HttpResponse response) {
		SimpleDateFormat dateFormatter = new SimpleDateFormat(HTTP_DATE_FORMAT, Locale.US);
		dateFormatter.setTimeZone(TimeZone.getTimeZone(HTTP_DATE_GMT_TIMEZONE));

		Calendar time = new GregorianCalendar();
		response.headers().add(DATE, dateFormatter.format(time.getTime()));
	}

	/**
	 * Sets the Date and Cache headers for the HTTP Response
	 *
	 * @param response
	 *            HTTP response
	 * @param fileToCache
	 *            file to extract content type
	 */
	private static void setDateAndCacheHeaders(FullHttpResponse response, File fileToCache) {
		SimpleDateFormat dateFormatter = new SimpleDateFormat(HTTP_DATE_FORMAT, Locale.US);
		dateFormatter.setTimeZone(TimeZone.getTimeZone(HTTP_DATE_GMT_TIMEZONE));

		// Date header
		Calendar time = new GregorianCalendar();
		response.headers().add(DATE, dateFormatter.format(time.getTime()));

		// Add cache headers
		time.add(Calendar.SECOND, HTTP_CACHE_SECONDS);
		response.headers().add(EXPIRES, dateFormatter.format(time.getTime()));
		response.headers().add(CACHE_CONTROL, "private, max-age=" + HTTP_CACHE_SECONDS);
		response.headers().add(LAST_MODIFIED, dateFormatter.format(new Date(fileToCache.lastModified())));
	}

	/**
	 * Sets the content type header for the HTTP Response
	 *
	 * @param response
	 *            HTTP response
	 * @param file
	 *            file to extract content type
	 */
	private static void setContentTypeHeader(FullHttpResponse response, File file) {
		MimetypesFileTypeMap mimeTypesMap = new MimetypesFileTypeMap();
		response.headers().add(CONTENT_TYPE, mimeTypesMap.getContentType(file.getPath()));
	}
}
